This invention relates in general to a method for rendering polyethylene oxide to a material of reduced crystallinity. More specifically, this invention relates to a method of forming a polymer composite comprising mixing smectite clay and polyvinyl pyrrolidone to form a first dispersion of intercalated clay, mixing said dispersion with polyethylene oxide to form a second dispersion, flowing said second dispersion into ketone so as to flocculate a polymer composite, and recovering said flocculate.
Polymers find a wide range of applications for use as films and coatings. In many instances, these films or coatings must be transparent. In addition to the transparency issue, these films or coatings should be able to be manufactured at a low cost and with as simple procedure as possible. For many polymers, transparent coatings or films can be generated but require melt extrusion or expensive organic solvents. It is preferable to be able to generate materials, which can be formulated using aqueous based systems. However, at high polymer concentration (greater than or equal to 50 weight %), many of these aqueous soluble/dispersible polymers will show significant crystallization upon drying, rendering the resultant films or coatings hazy due to light scattering from the crystallites in the polymeric film.
Polyethylene oxide polymers are high molecular weight water-soluble polymers with a wide variety of applications. Some of these applications are detailed in product brochures of Union Carbide for their Polyox water-soluble resins. According to such product literature, polyethylene oxide can be used as binders for pigments, fillers, metal powders, and ceramics with application in battery electrodes, cathode ray tubes, and fluorescent lamps. The strong hydrogen bonding affinity of polyethylene oxide accounts for its association with various polar compounds, such as phenolic resins, mineral acids, halogens, ureas, lignin sulfonic acids, and poly carboxylic acids. These novel complexes can be discrete chemical entities with unique properties with application in batteries, microencapsulated inks, slow release bacteriostats, water soluble adhesives, etc. Polyethylene oxide can form water-retentive gels with application as absorbent pads and diapers. Polyethylene oxide can be used as emollient in cosmetic and hair products. Most importantly, polyethylene oxide can be formed into flexible films both by thermoplastic processing and casting techniques, providing wide latitude of applications. As thermoplastics, these films are readily calendered, extruded, molded, or cast. Sheets and films of polyethylene oxide can be oriented to develop high strength. Polyethylene oxide films are inherently flexible and tough, and resistant to most oils and greases. Polyethylene oxide can be used alone or blended with a wide variety of other polymers such as polyethylene, polystyrene, polycaprolactone, ethylene vinyl acetate, nylon, etc. In packaging, polyethylene oxide can be used to provide heat-sealability, hot melt adhesion, improved resistance to humidity, lubricity, controlled release, bio-degradability, and non-toxicity. However, as noted in the product literature, polyethylene oxide, particularly the higher molecular weight grades, retains a very high degree of crystalline character at temperatures far above the melting point. This retained crystallinity renders these materials unsuitable in applications requiring transparency for aesthetic or optical reasons.
Additional applications of polyethylene oxide include U.S. Pat. No. 5,143,071 which describes the formation of non-stringy adhesive hydrophilic gels using polyethylene oxide and water or polyvinyl pyrrolidone, and may have a water-soluble electrolyte added to provide conductive non-stringy adhesive materials for medical electrodes. To make effective, these polymeric mixtures must be cross-linked using exposure to radiant energy, then remain tacky such that the adhesive can adhere to a subject""s skin without discomfort.
U.S. Pat. No. 5,866,292 describes a liquid developer composition with a copolymer, where a charged liquid developer is comprised of a nonpolar liquid, thermoplastic resin particles, pigment, a charge director, and a charge control agent comprised of a polyethylene oxide:polypropylene oxide blend in a solid form.
A resin for paper making is described in U.S. Pat. No. 5,866,669. Sulfonated phenol-formaldehyde is combined with polyethylene oxide to yield a paper, which has long life and improves the yield of fine fiber and filler reducing the water treatment waste load. Another polyethylene oxide application for paper manufacture is described in U.S. Pat. No. 5,578,168 where polyethylene oxide is dispersed with a salt to form a suspension with at least 15% polyethylene oxide by weight. The said suspension prevents the loss of fiber fines during paper manufacture and resists viscosity loss.
A thermoplastic composition is described in U.S. Pat. No. 6,010,971 where polyethylene oxide is mixed with a multicarboxylic acid (ex: adipic acid). Such a material can be extruded into fibers and formed into a nonwoven structure and may be used for disposable absorbent products intended for the absorption of fluids such as body fluids. A similar application can be found in U.S. Pat. No. 5,916,969 where polyethylene oxide is blended with polyolefins for disposable absorbent articles such as a diaper or feminine pad. Such a material can be produced only under melt conditions.
U.S. Pat. No. 5,618,316 describes an invention to provide an intraocular lens having improved biocompatibility achieved by applying a polyethylene oxide coating to the lens surface through covalent bonding.
U.S. Pat. No. 5,589,545 describes molded polymer blends which become lubricious when exposed to water with end uses in personal care articles, e.g., lubricious strips for razors, and in medical articles, e.g., catheters.
U.S. Pat. No. 5,011,814 describes a dye-receiving element for thermal dye transfer including a support having on one side thereof a polymeric dye image-receiving layer and on the other side thereof a backing layer made from a mixture of PEO and submicrometer colloidal inorganic particles.
U.S. Pat. No. 5,674,578 describes water soluble/dispersible multilayered film of high interlayer adhesive strength and collection pouches formed therefrom, with high load bearing capacity but easily disposable.
In the literature, examples are provided where PEO is blended with clay materials for the purpose of obtaining enhanced properties such as modulus. Lerner and coworkers (Chem. Mater., (1993), 5, p. 835; Elect. Acta, (1995), 40, p. 2245) described the generation of polyethylene oxide and Na-montmorillonite clay nanocomposites where the polyethylene oxide and clay were added to water. After 24 hours of stirring, followed by vacuum drying, they were able to successfully intercalate PEO into the clay lattice up to 30 wt. % polyethylene oxide. However, at polyethylene oxide levels greater than 30 wt. %, crystalline polyethylene oxide was observed. Giannelis and coworkers (Adv. Mater., (1995), 7, p. 154), working on polymer electrolyte nanocomposites, observed similar intercalation effects when they worked with polyethylene oxide and Na or Li exchanged silicate clays. In their materials preparation, montmorillonite clay (28 wt. %) was mixed with PEO and annealed for 6 hours at 80xc2x0 C. Before annealing, crystalline polyethylene oxide was observed to be present in the sample. After the long annealing time, the crystalline PEO was not observed indicating that it had intercalated inside the clay. Like Lerner, Giannelis found that at a higher clay level, 40 wt. %, crystalline polyethylene oxide was present that did not intercalate the clay. A method of making clay-polyethylene oxide nanocomposites using acetonitrile as the solvent is described by Schmidt-Rohr and coworkers (Macromol., (1999), 32, P. 6718). They, like Giannelis, also found that when polyethylene oxide is at a 40 wt.% level in the nanocomposite, excess crystalline polyethylene oxide could be detected. Doeff and Reed (Sol. State Ion., (1998), 113-115, P. 109) describe a very laborious and time-consuming method of attempting to produce high weight percent polyethylene oxide nanocomposites. A 1 wt. % clay in water solution was stirred for one-half hour followed by the addition of LiCl to make a 1 molar solution. This solution was then stirred for a minimum of 48 hours. The suspension that was created was then dialyzed to remove salt. Polyethylene oxide was then added and stirred for an additional 24 hours. Solutions were then coated on glass and dried at 120xc2x0 C. for a minimum of 48 hours. However, samples at 70 wt. % polyethylene oxide were found to contain crystalline polyethylene oxide in addition to the intercalated clay.
Use of polyethylene oxide, with and without various addenda, in ink jet applications can be found in related patent literature (e.g., U.S. Pat. Nos. 5,888,635; 5,688,603; 5,781,216; and EP 0 732 218 A1). However, the issue regarding the degree of crystallinity of polyethylene oxide is neither resolved nor adequately addressed.
It is clear that although the prior art is replete with numerous applications utilizing polyethylene oxide, there remains an important need for further innovation for a method of generating reduced crystallinity polyethylene oxide-containing materials. Reduced crystal materials are more transparent. Additionally, there is a need for producing polyethylene oxide-containing materials which can be used as coatings and films, with reduced or no haze, resulting from reduced polyethylene oxide crystallinity, using materials of modest cost and in a simple and economic process.
There remains a need for a nanocomposite material with reduced crystallinity polyethylene oxide, in particular, nanocomposite materials containing a smectite clay, polyvinyl pyrrolidone, and polyethylene oxide.
It is an object of the invention to provide a method for producing improved nanocomposite materials containing polyethylene oxide, smectite clay, and polyvinyl pyrrolidone.
It is another object of the invention to reduce or eliminate the crystallinity of the polyethylene oxide in nanocomposite materials where the weight fraction of polyethylene oxide is greater than 50%.
It is another object of the invention to reduce or eliminate the haze in articles, especially films and coatings, generated from nanocomposite materials where the weight fraction of polyethylene oxide can be greater than 50%.
These and other objects of the invention are accomplished by a method of forming a polymer composite comprising mixing smectite clay and polyvinyl pyrrolidone to form a first dispersion of intercalated clay, mixing said dispersion with polyethylene oxide to form a second dispersion, flowing said second dispersion into ketone so as to flocculate a polymer composite, and recovering said flocculate.
This invention provides nanocomposite materials for articles, especially films and coatings, which have transparency or reduced haze. The nanocomposite materials formed by the invention have improved mechanical properties, as well as being more transparent than prior polyethylene oxide polymer materials. It is surprising that haze reduction in the polyethylene oxide occurs when an intercalated clay is added to make a nanocomposite material. The materials of the invention find use as hydrophilic layers. They are particularly useful in overcoats for ink jet, other printing papers, and transparency display materials. They also may be used as hydrophilic layers on cutting devices, such as razor blades.